the manga must be much more faster than anime because one anime episode is made by 3-4 manga episodes
that is one of the reasons that the long animes have always filler episodes.....just like BLEACh and Naruto

Well I'm guessing it's because animes are always based on the manga and hardly ever the other way round.

Not necessarily true (there are more than a few manga out there based on anime), but in the case of the anime series trying to remain true overall to the original manga story, it may be forced to "wait" or go with "fillers" - especially if both versions are still ongoing. Plus, making an anime series requires more time, people, and resources compared to the manga.